1. Field of the Invention
The present disclosure relates to a solid-state imaging apparatus.
2. Description of the Related Art
In recent years, as a solid-state imaging apparatus, a CMOS solid-state imaging apparatus including an amplifying element in a pixel in an imaging region has become widespread. The CMOS solid-state imaging apparatus is configured so that each of pixels arranged in a matrix includes a photoelectric conversion element and an amplifying element, and an amplified photoelectric conversion signal is read by a vertical signal line shared by each column. Each vertical signal line has a current source, and the amplifying element that is usually an MOS transistor performs a source follower operation to amplify signals. Japanese Patent Application Laid-Open No. 2004-165825 discloses an example thereof.
However, Japanese Patent Application Laid-Open No. 2004-165825 has a problem as described below. First, a current source circuit connected to each vertical signal line is arranged in one dimension in a horizontal direction. A current supplied by current source circuits of the number of columns is supplied to a ground line, and wiring resistance of the ground line increases a ground potential that is originally 0 V. The increase in the potential may change a gate bias voltage of a MOS transistor that constitutes a current source, and shift an operation point of a pixel source follower. This may degrade linearity of a circuit operation and cause shading of an image.
Second, a gate bias line of a current source circuit (hereinafter referred to as a gate bias line) extends long in a horizontal direction of a screen. Thus, if the solid-state imaging apparatus is used, for example, in a digital camera or a digital video camera, a current due to electromagnetic induction, which is caused by magnetism generated when a lens driving motor near an imaging device is operated, may be supplied to a gate line. The induced current causes variations in gate potential, and changes a pixel output, which may cause noise referred to as “white stripe or smear of a horizontal direction” in an image.
Such a phenomenon has become prominent with remarkable development in sensitivity of a digital camera or a digital video camera in recent years. Specifically, minute potential variations of a gate bias line tend to be viewed as degradation in image quality in high sensitivity setting.